The outcomes for acute myeloid leukemia (AML) have remained abysmal for the past 30 years. 20- 40% of patients fail to achieve remission with induction chemotherapy, and 50-70% of patients who achieve a complete remission relapse within 3 years. While cytogenetics are the backbone of risk-stratification, nearly 50% of AML cases are cytogenetically normal (CN-AML) and, biologically and clinically, the most heterogenous group. The nucleo-cytoplasmic shuttle protein nucleophosmin (NPM1) is mutated in 50% of CN-AML cases resulting in the nuclear export of this protein. This has been shown in large clinical cohorts to confer a favorable prognosis and obviates the need for a bone marrow transplant in these patients. This subset of AML has been recognized in a unique diagnostic category in the WHO 2008 classification of hematologic malignancies. The mechanism by which mutated NPM1 (NPM1mut) confers this advantage in CN-AML is unclear. It has previously been hypothesized that NPM1mut dislocates other protein partners into the cytoplasm and consequently affecting their function. We have previously demonstrated that FOXM1, an oncogenic transcription factor, co-localizes with NPM1 in cancer cells. In this proposal, using a novel multispectral imaging modality we will study the cellular interaction of FOXM1 and NPM1 in AML primary blast cells. We will also investigate the functional significance of FOXM1 localization in this disease using AML cell lines. Importantly, we will assess the clinical correlation of mislocalized cytoplasmic FOXM1 with outcomes in AML with the goal of examining its role as a favorable prognostic marker in CN-AML. We intend to show that FOXM1 is the oncogenic driver dictating prognosis in AML. Mutations in NPM1 resulting in its nuclear export mislocalizes FOXM1 to the cytoplasm where it is inactive as a transcription factor. This may account for the improved outcome in this sizeable subset of AML patients. In several AML cell lines we will test how FOXM1 knockdown or FOXM1 overexpression will affect sensitivity to chemotherapeutic drugs in vitro and vivo. We will determine whether FOXM1 knockdown in AML cell lines with nuclear localization of FOXM1 makes them more sensitive to chemotherapy. Nude mice will be injected with AML cell lines with stable FOXM1 knockdown or OCI-AML3 cell line with stable FOXM1 knockdown or with FOXM1 overexpression, and with control cell lines to establish xenograft tumors. We expect that FOXM1 knockdown in U937 and HL60 AML cell lines will increase sensitivity to treatment in xenograft tumors induced by these AML cell lines. I contrast, suppression of FOXM1, localized in the cytoplasm, in OCI-AML3 cell line would not affect sensitivity to chemotherapy in xenograft tumors induced by this cell line. The experiments described in our proposal will reveal if cytoplasmic FOXM1 is a novel favorable prognostic factor in AML and whether nuclear expression of FOXM1 determines the resistance of xenograft tumors induced by AML cell lines to chemotherapy.